The term wax is a collective term for a series of natural and synthetic substances. Generally understood by this term are materials which are already easily plastically mouldable below their melting range or softening range, have a translucent to opaque appearance, melt without decomposition above 40.degree. C. and already produce liquids of relatively low viscosity slightly above the melting point and which possess a greatly temperature-dependent consistency and solubility. Furthermore, waxes can mostly be polished under light pressure (Ullmann's Enzyklopadie der Technischen Chemie, 4th edition, volume 24, Verlag Chemie, Weinheim 1989).
Waxes are used in the dental field as modelling, casting, occlusion or adhesive waxes. Mixtures of natural waxes and synthetic waxes are used almost exclusively, the physical properties of the waxes being geared to the desired use (K. Korber, K. Ludwig, Zahnarztliche Werkstoffe und Technologie, G. Thieme Verlag, Stuttgart, 1982, page 90). For example, a modelling wax suitable for modelling preshaped parts should be easy to mould and have as good a dimensional stability as possible at the temperature of the mouth. Mixtures of paraffin wax, stearin wax, Japan wax and beeswax are suitable for this purpose.
Conventional waxes are generally heated for processing. Curing takes place by the wax solidifying on subsequent cooling. In this case, relatively large, uncontrollable volume changes generally occur. Furthermore, conventional waxes have the disadvantage that they easily break when being removed from the model and change their shape under even relatively slight mechanical and above all thermal stress.
In order to avoid these disadvantages, mixtures of natural and partially or wholly synthetic waxes with polymerizable monomers or oligomers such as polyfunctional acrylates and methacrylates have recently been used. These mixtures can be specifically cured after treatment and then have a higher mechanical stability than the pure waxes.
For example, mixtures of polyethylene waxes with styrene or acrylate monomers are disclosed in JP-A-92/4748 (C.A. 120 (1993) 136156) and JP-A-91/330047 (C.A. 119 (1993) 282306). Furthermore, photopolymerizable waxes for the dental field based on mixtures of natural or synthetic waxes with conventional acrylic compounds and photoinitiators are described in JP-A-90/312256 (C.A. 128 (1992) 27523). The disadvantages of these mixtures are that conventional dental waxes and dental crosslinker monomers do not mix well with one another and that above all the wax is not incorporated into the polymer network on polymerization. The result may therefore be the formation of wax domains, i.e. a multiphase system is formed, the mechanical strength of which is accordingly low.
EP-B-0 110 193 discloses wax-free wax substitutes for producing casting models. These compositions are based on mixtures of di- or polyfunctional meth- or acrylic acid esters, a photoinitiator and optionally a photoactivator and organic fillers. On account of the composition of the materials claimed in EP-B-0 110 193, they do not exhibit any wax-like properties, i.e. the materials cannot be modelled like waxes and consequently the dental technician must replace the usual wax technique with a layer technique which involves a lot of work. Changes or adjustments to the model can then no longer be made, since curing takes place by polymerization after application of the respective layer. Furthermore, this process has the disadvantage that thin layers can only be produced using slightly filled or unfilled mixtures of di- or polyfunctional (meth)acrylic acid esters, during the polymerization of which a considerable volume contraction results.
EP-B-0 380 116 discloses mixtures which, in order to influence the expansion behaviour of the moulding compounds, additionally contain an organic compound having a boiling point and/or a sublimation point in the range above 150.degree. C. and which does not react with the organic polymerizable composition. The named compositions are characterized in particular by the fact that they leave no residues upon combustion.
U.S. Pat. No. 5,403,188 discloses thermoplastic moulding compounds which are suitable for the production of dental impressions. The compounds contain a polymeric thermoplastic material, preferably a polycaprolactone, a polymerizable resin, an initiator and optionally a filler. They are solid at 38.degree. C. and practically not mouldable and they are heated for processing. Curing then takes place by cooling. After the impression has been produced, the compounds are additionally cured by a radical polymerization. The materials have the disadvantage that they only melt down to form highly viscous products. Dental shaping is extremely difficult since the materials are not only viscous in the molten state, but also very sticky.
It is the object of the invention to provide wax-like dental materials which do not have the above-named disadvantages and are also suitable in particular for producing temporary and permanent prostheses.